The genomic sequence of an Australian isolate of carrot mottle umbravi
rus (CMoV-A) was determined from cDNA generated from dsRNA. This provi
des the first data on the genome organization and phylogeny of an umbr
avirus. The 4201-nucleotide genome contains four major open reading fr
ames (ORFs). Analysis suggests that ORF2 encodes an RNA-dependent RNA
polymerase, that ORF4 encodes a movement protein, and that the virus h
as no coat protein gene; The functions of ORFs 1 and 3 remain unknown.
ORF2 is probably translated following ribosomal frameshifting. ORFs 3
and 4 are probably translated from a subgenomic mRNA. Sequence compar
isons showed CMoV-A to be closely related to pea enation mosaic RNA2 (
PEMV-RNA2), but also to have affinities with the Bromoviridae. These f
indings shed light on the relationships between the luteoviruses, PEMV
, and the umbraviruses and on the relationships between the carmo-like
viruses and the Bromoviridae. (C) 1996 Academic Press, Inc.